Listen To The Pump Master, His Story Never Wears Down

Example of a worn impeller at the Damen Dredging Experience
Example of a worn impeller at the Damen Dredging Experience

This week is the triannual WODCON conference1. This edition will be held in lovely Copenhagen, in itself already a reason to be there. But there is more, the program is packed with interesting items. Starting with the opening ceremony with the Danish minister of transport and the Corporate Executives Discussion on sustainability. The Fehmarnbelt Tunnel Link will be a hot topic all through the program. My personal suggestion would be to attend Session 4: ‘Hydraulic Transport’ on Tuesday 17. Two of my highly regarded colleagues will be presenting their work on very interesting topics.

Damen colleagues present at the WODCON 2022, (l) Rick Bekkers, (r) Suman Sapkota
Damen colleagues present at the WODCON 2022, (l) Rick Bekkers, (r) Suman Sapkota

Rick Bekkers has been involved in the development of our new ProDredge edition. It is a slurry transport estimation tool. Where Ewout van Duursen has been working tirelessly on programming the tool, Rick has been checking the models and the results against known literature. He will show you the new reports generated and the insights they will give you for evaluating a proposed dredging system.

ProDredge presentation of a dredging system to be evaluated
ProDredge presentation of a dredging system to be evaluated

Suman Sapkota will be presenting his favourite topic: ‘Erosion estimation on the impeller blades of centrifugal dredge pumps’. He has been working on this topic ever since his own graduation project.2 Over the years he spend pondering over this issue and gradually grew in experience with the problem. Based on his ideas, he managed to start a cooperation with the Delft University of Technology and have a master student working on the practical details of his plans. Previously, I’ve written about the graduation of Wim Kleermaker in another article.3

Wim Kleermaker during the practical phase of his graduation in dredging
Wim Kleermaker during the practical phase of his graduation in dredging

Suman has been concentrating on gathering the various models for wear under different conditions during his own graduation. The results from his simulations could only be checked against my own experience with badly worn impellers and disasters. Immediately introducing observer bias and survivor bias. So, for this project Suman really wanted to include experiments to have at least one observation to match the simulations.

Damen slurry test circuit with dredge pump and impeller
Damen slurry test circuit with dredge pump and impeller

And what a struggle it was, to get the experiments done. Wim really gained more experience in fixing troubles than in fact finding. In the end he managed. After operating for a couple of weeks under heavy load conditions for the dredge pump, the impeller showed a noticeable wear pattern. And they came up with an innovative way of measuring the erosion pattern and match the test results with the simulation results.

Comparing CFD results (l) with measured erosion (r)
Comparing CFD results (l) with measured erosion (r)

The paper Suman is going to present on the WODCON, condenses the results from Wim together with Suman’s previous work as a graduation student himself. Don’t get deterred by the in depth analysis. If you fancy, you can follow the comprehensive literature references and understand his model. Or, just enjoy the ride and inspect the interesting pictures with the conclusions at the end. If you are really interested in his work, just approach him in the break hours, he is very willing to share his experience with you.

If you can’t find him, or Rick. Drop by at our booth #27 in the lobby.4 There will always be someone to get you into contact.

Damen invitation for the WODCON 2022
Damen invitation for the WODCON 2022

References

  1. WODCON 2022, WODA
  2. Graduation Suman Sapkota: Where Wear Parts Were Worn Down, Discover Dredging
  3. Graduation Of Wim Kleermaker: Measuring And Predicting Wear In Impellers
  4. WODCON Dredging Conference, Saskia den Herder

See also

Graduation Of Wim Kleermaker: Measuring And Predicting Wear In Impellers

Wim Kleermaker during the practical phase of his graduation in dredging
Wim Kleermaker during the practical phase of his graduation in dredging

Yesterday, Wim Kleermaker graduated at the TU Delft on a research project he conducted on our slurry test circuit at Damen Dredging Equipment. Specifically, he was investigating the wear behaviour in our dredge pumps. The noteworthy aspect of this project, was that Wim was supervised by our colleague Suman Sapkota. As long time readers in the audience might remember Suman was my own pupil some years ago1.

Example of a worn impeller at the Damen Dredging Experience
Example of a worn impeller at the Damen Dredging Experience

Wear is a very common process in the dredging industry and one of the main cost factors in a project2. It is beneficial to know the amount of wear to expect in a certain condition and be able to predict the budget to reserve for this nuisance. This is only possible when we as a manufacturer will be able to predict the wear rate and pattern can provide the information to the operator for his estimates. We do have historical data that will allow us to provide a ball park figure, but a more analytical approach might assist us in particular unusual cases. Furthermore, it will also provide us insight in the impact of certain design decisions for the wear performance of a certain pump design. For Wim’s graduation, he had to approach this academically: come up with a simulation model and verify this with measurements.

Damen dredge pump slurry test circuit on the outfitting quay in Nijkerk
Damen dredge pump slurry test circuit on the outfitting quay in Nijkerk

The measurements were done in our slurry pump test circuit. This circuit has been highlighted a couple of posts back3. For Wim’s experiments, he used an impeller under a certain operating condition and mixture properties. Before and after a representative period, the condition of the impeller was measured and the difference is a measure of the wear experienced.

CFD result for the wear experiments
CFD result for the wear experiments

Wear (or scientifically: erosion) is related to the impact of the particles on the material surface. In order to know the kinetic energy of the particles, the flow field has to be known. As the flow fleild cannot be measured directly at the test circuit, we have to resort to Computation Fluid Dynamics. We already know of Suman’s graduation, to look for patterns in the flow lines, but Wim has extended the procedure to also quantitively estimate the related erosion.

Comparing CFD results (l) with measured erosion (r)
Comparing CFD results (l) with measured erosion (r)

Although there is only a limited amount of data available, comparing the results of the CFD estimation and the measured erosion are looking promising. This is certainly a workflow that will provide us the unique tools for engineering better pumps and assisting customers in their specific projects.
Although Wim will not join our ranks in the dredging community and pursue a different career in another interesting industry, we are sure he will be constructive and dedicated colleague at Marin.

Another master and student fighting evil forces (Credit: Star Wars)
Another master and student fighting evil forces (Credit: Star Wars)

References

  1. Graduation Suman Sapkota: Where wear parts were worn down, Discover Dredging
  2. Wear parts, Discover Dredging
  3. Student Interviews On Their Projects With Our Dredge Pump Slurry Test Circuit In Damen Nieuws, Discover Dredging

See also

Super Materials To Improve Lifetime When Your Pump Is On Acid

Severely corroded impeller next to the original wear part
Severely corroded impeller next to the original wear part

Recently I had a discussion on LinkedIn about the pump killer #2: ‘wrong material’. There I chipped in with this disaster picture1. It was an application where we provided a suboptimal material for the acid environment. The consequences were disastrous, as seen above. Luckily, we were able to identify the problem and propose a different material. Now, I want to share our experience here, also.

What was the case? A client requested a DOP for handling tailings in their facility. Tailings is fine stuff. Leftover from mining or waste water processing. We are always careful on the grain size, as these fines may interfere with the operation of the mechanical seal. With appropriate measures, they can handle them. As the grains tend to be fresh, they can be razor sharp. The erosion on the wear parts is higher than normal fine silt. Oh, and most tailings come with acid in their water.

So, for this request we proposed a material that was usually good in wear resistance and had a moderate resistance against corrosion. Casting materials can be classified for their corrosion resistance with the Pitting Resistance Equivalent Number2. This PREN can be calculated with:

PREN = Cr + 3.3Mo + 16N

Two observations to this formula. One, this is only valid for normal Chromium content materials intended as Stainless Steel. Two, it does not mention the aggression of the corrosion. The acidity is usually provided in the request for quotation. But, a catalyst for the oxidising reaction is the conductivity of the fluid. Chloric acid and sulphuric acid may have the same pH, but due to their different ion and electron content, their conductivity differ. We did not check this in the above example, with the consequences in the picture.

Is increasing the chromium content in the wear alloy a solution to this corrosion problem? Mwah, moderately. Alloys like stainless steel profit from the above approach. But, wear materials use their Chromium for generating carbides. Those are the particles we require for the wear resistance. The Chromium provided is than not available for corrosion resistance. e.g. White cast iron with 3%C and 21%Cr will only have about 6% of Chromium to be used in the PREN. For white cast irons, it is better to use the following graph3 to find their corrosion resistance.

Corrosion Properties of Cast Iron Ball Materials in Wet Grinding. (Credit: Corrosion Feb 1992)
Corrosion Properties of Cast Iron Ball Materials in Wet Grinding. (Credit: Corrosion Feb 1992)

If corrosion is such an issue, why don’t we use Stainless Steel? Well, there you bite yourself in the tail. Stainless Steel in itself is relatively soft. It would have the same wear index of normal construction steel. By definition a Wear Rate Index of 1. For the sharp tailing material, that would be disastrous in itself. But, let’s play along. The stainless steel derives it’s corrosion resistance from the Chromium as explained before. Chromium’s trick is to generate a clear closed patina layer of Chromium Oxide protecting the underlaying material. In dredging conditions, the particles damage the protecting patina forever exposing fresh base material for more erosion and corrosion. In the end, the wear is accelerated and part life decreases dramatically.

Accelerated erosion process under corrosive conditions
Accelerated erosion process under corrosive conditions

Back to the pictured example, we expected some corrosion, but did not expect the higher conductivity. So, after three weeks, the client noticed a sudden los of performance. The leading edge of blades and the hub shroud were completely eaten away. As long as the trailing edge was there, it generated head. A single stone hit severed the front of the impeller from the hub and we received the above disaster picture. After damage evaluation, we sent a CW250 impeller and that one lasted.

A corrosion resistant DOP working in an acid tailings pit
A corrosion resistant DOP working in an acid tailings pit

References

  1. Pump killers: How to fight the 13 most common centrifugal pump failures? Number 2., Jos Overschie
  2. Pitting resistance equivalent number, Wikipedia
  3. Corrosion Properties of Cast Iron Ball Materials in Wet Grinding, Corrosion

See also